Dear all, apologies for a newbie question, but I am returning to Haskell after years of hiatus and Java... I have the following data type (representing geometries): data Geometry = Point FID Coordinate | LineSegment FID (Coordinate,Coordinate) | Polyline FID [Coordinate] | Polygon FID [Coordinate] deriving (Show,Eq) type Coordinate = (Float, Float) And this is where I fail: I have no idea how to type getCoordinates, in order to match against the three different combinations -> it can result into a Coordinate, or a typle, or a List. I am sure it is possible! class Geoms a where getCoordinates :: a -> b instance Geoms Geometry where getCoordinates (Point _ a) = a getCoordinates (Polygon _ a) = a And I want to access the Coordinates for each given geometry. Note that I tried to define it using records: say, Polygon {getID::FID,gcoords::[Coordinate]}, but the coords function failed to match, due to having different return types for Geometry. Thank you very much, Martin